apt "dpkg was interrupted, you must manually run dpkg --configure -a": finish what was started

1. Run it

sudo dpkg --configure -a

This finishes setting up everything left half-done. It may take a while and print a lot, and it may ask you questions about config files. Let it finish. If you’re on SSH, use tmux, so a dropped connection can’t interrupt it again.

Then let apt finish what it planned:

sudo apt --fix-broken install
sudo apt update
sudo apt upgrade

2. If it says another process holds the lock

dpkg: error: dpkg frontend lock was locked by another process with pid 2143

Something else is working, often unattended-upgrades on a server. Wait for it, and don’t delete lock files. See could not get lock.

3. If the disk is full

A full disk is a common cause of the interruption itself, and running this again fails the same way:

dpkg: error processing archive ... (--unpack):
 cannot copy extracted data for './usr/lib/...' to '...': failed to write (No space left on device)

df -h / /boot
df -i /

/boot is the usual culprit on Ubuntu, filling up with old kernels. Free space first, then run it again:

sudo apt clean
sudo journalctl --vacuum-size=200M
sudo apt autoremove --purge

If autoremove can’t run because of the broken state, list kernels with dpkg -l 'linux-image*'. Never remove the one you’re running, which uname -r shows. For more, see no space left on device.

4. A package that fails

Often one package’s own setup script is what fails:

Setting up mypackage (1.2.3) ...
Job for mypackage.service failed because the control process exited with error code.
dpkg: error processing package mypackage (--configure):
 installed mypackage package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 mypackage

That’s the key: the last lines name it, and post-installation script tells you where. Here, a service wouldn’t start. Read why:

sudo journalctl -xeu mypackage --no-pager | tail -n 30

See Job for service failed. A service that already uses a port, or a broken config file, is common. Fix that, and run sudo dpkg --configure -a again.

Or if you don’t need it, remove it:

sudo apt remove --purge mypackage
sudo dpkg --configure -a

If apt won’t remove it, dpkg can:

sudo dpkg --remove --force-remove-reinstreq mypackage

Only use that for the one named package. Don’t use it on system packages such as libc6 or systemd.

5. Conflicts between files

dpkg: error processing archive /var/cache/apt/archives/foo.deb (--unpack):
 trying to overwrite '/usr/bin/foo', which is also in package bar

Two packages claim one file, often through a third-party repository. See which you have, and remove or update the one you don’t need:

dpkg -S /usr/bin/foo
apt-cache policy foo bar

6. Check the state

When it’s all done, this should print nothing:

sudo dpkg --audit
dpkg -l | grep -vE '^(ii|rc)' | tail -n +6

In the second, ii means fine, and rc means removed with its config left behind. Anything else, like iU or iF, is half-finished.

If it happened during a release upgrade, don’t reboot yet, as the machine may not start: finish this, and check sudo do-release-upgrade afterwards.